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Longitudinal air permeability measurements of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] outer sapwood from three trees of different seed sources and growth locations were determined on microsections about 500-700 microns thick, dried by air-seasoning and solvent-seasoning. The specimens were successively reduced in length from 3.6 to 0.4 cm. Darcy's law was found to be invalid with respect to specimen length. Sapwood earlywood longitudinal air permeability was found to be a sensitive barometer of seasoning effect on pit aspiration. The objective was to determine where the variations in margo porosity were significant, and hence applicable to problem of Douglas-fir permeability. The diameters of earlywood margo openings were measured directly from electron micrographs of un-aspirated (solvent-seasoned) pits. The margo measurement was assumed to represent one plane instead of the actual three dimensional structure, and the pores observed were the ones that controlled the rate of flow. Samples from the most, intermediately and least permeable specimens were selected and prepared for the evaluation of anatomical parameters of bordered pit membranes (margo area and margo porosity) as related to permeability. The effects of pit aspiration, tracheid length, total number of pits per tracheid, number of tracheids per square millimeter, and specific gravity on permeability were also assessed. Pit partial aspiration was found as the most important variable correlated with permeability. In an order of decreasing importance, pit partial aspiration, margo porosity and specific gravity together accounted for 94 per cent of total variability in permeability of solvent-seasoned earlywood. No statistical evaluations were made to compare the three trees with respect to their permeability and the measured parameters. / Forestry, Faculty of / Graduate

One of the major processes in lumber industry is wood drying. This process consumes large amounts of energy and capital, and due to the length of time it takes, it acts as a governing factor in lumber production levels. Development of improvements in processes and equipment used in wood drying can be expedited through computer simulation of various drying procedures. These numerical simulations depend on the accuracy of numerical models representing wood transport properties, including functional dependency of liquid permeability through wood with respect to local saturation level. Data available in the literature mainly represent wood permeability properties at fully saturated levels. This is an indication of steady state flow methods used in determining these values which are based on wide spread use of similar methods utilized in studies on fluid flow through soil. This research determines unsaturated wood permeability using transient liquid flow methods that are more representative of actual drying process. Initially saturated wood samples are spun in a low speed centrifuge to induce liquid migration through the cell structures. Transient local moisture profiles along the sample are measured using a scanning gamma ray densitometer. Numerical integration and curve fitting procedures are used to process these data. Finally, utilizing liquid continuity equation the functional dependency of permeability with respect to saturation is calculated. Some permeability results appear to be reasonable when compared with actual wood behavior during drying. Measurement procedures prove to yield accurate results for moisture content and saturation levels in wood with less than 5% relative error in average saturation level of .75. However, due to natural inhomogeneities in wood cellular structure, the final calculated results for unsaturated permeability show high levels of uncertainty (up to 112% relative error).

The longitudinal air permeabilities of the wood of 1116 specimens from 279 trees, two sapwood and two heartwood replicates, representing two varieties of lodgepole pine (Pinus contorta, vars. latifolia and murrayana) were measured with a steady state apparatus. It was found that the mean ratio of sapwood to heartwood permeability was ca. 10:1 for both varieties. The mean ratio of var. latifolia to murrayana was 1.5:5 and 1.75:5 for sapwood and heartwood, respectively. The most important source of variation following the difference between heartwood and sapwood was that among trees. Geographical locations, such as latitude and elevation did not significantly influence permeability. Tree size did, but only because the small trees (3 inch diameter) showed higher heartwood permeability and lower sapwood permeability than normal. Ca. 20 specimens of latifolia heartwood showed extremely high permeabilities. They were also deeply brown in color, which probably was caused by fungal or bacterial infestation. Pit pore size and number per cm² were determined for sapwood by making four permeability measurements, each at a different average pressure on each specimen. A mean pit pore radius of 1.5 µm and 1.3 µm for sapwood of var. latifolia and var. murrayana was calculated. The median values between 1200-1300 pit pores per cm² indicate an average rate of tracheid connection of 1.2-1.3%. Of the tested wood parameters including moisture content and specific gravity average ringwidth, only the permeability of var. latifolia was significantly correlated with moisture content for both heartwood and sapwood, with a negative correlation coefficient. Water retention measurements were carried out to relate the measured gas permeability of an individual specimen to its ability to absorb water. For both varieties the retention was significantly and quadratically correlated with sapwood permeability (R² = 0.286 and 0.224) and was linearly correlated with heartwood permeability (R² = 0.488 and 0.5775). The correlation factors for the regression between retention and the logarithm of permeability were 0.239 and 0.227 for sapwood and 0.447 and 0.420 for heartwood. / M.S.